Dan, This information was in a TUV Newsletter last year.
Brian Transient Suppressors according to EN60950 CCA doc section 1.5 ACROSS THE MAINS Transient suppressors can be connected across the mains if it is separately approved to IEC 1051-1 and IEC 1051-2 (or CECC 42200). If it is not separately approved, then a short-circuit protective device (such as a fuse) is required. BETWEEN LINE AND GROUND (PE) It is NOT recommended that Transient suppressor are used between Line and Ground due to the many safety issue it generates: varistors has the tendency to generate excessive leakage current within a few years of use, and a varistor from line to ground will cause a false production High Pot test failure. Transient suppressors can only be connected from Line to Ground (Protective Earth) on pluggable equipment if a gas tube and fuse is in series with the varistor (transient suppressing device). To solve the High Pot problem, some companies install a special screw in the back on the unit that opens the ground connection to the transient suppressing device when the screw is removed. If this approach is taken, it must be well documented in the User's documentation. Surge Suppressors are allowed from line to ground on Permanently connected equipment. ____________________Reply Separator____________________ Subject: Varistor to Ground Author: dk...@intetron.com List-Post: emc-pstc@listserv.ieee.org Date: 4/19/02 3:28 PM Hi all, Is it generally permissible to put a varistor (MOV) across the 120 Vac line and ground for surge suppression/line conditioning products? I can see some potential safety implications here if the MOV shorts but I am interested in how this is addressed in the relevant safety standards. Dan Kwok Principal Engineer http://www.intetron.com ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"